88 documents found, page 1 of 9
Time-limited Bloom Filter
Rodrigues, Ana; Shtul, Ariel; Baquero, Carlos; Almeida, Paulo SérgioA Bloom Filter is a probabilistic data structure designed to check, rapidly and memory-efficiently, whether an element is present in a set. It has been vastly used in various computing areas and several variants, allowing deletions, dynamic sets and working with sliding windows, have surfaced over the years.When summarizing data streams, it becomes relevant to identify the more recent elements in the stream. Ho...
Using survey data to estimate the impact of the omicron variant on vaccine effi...
Rufino, Jesús; Baquero, Carlos; Frey, Davide; Glorioso, Christin A; Ortega, Antonio; Reščič, Nina; Roberts, Julian Charles; Lillo, Rosa ESymptoms-based detection of SARS-CoV-2 infection is not a substitute for precise diagnostic tests but can provide insight into the likely level of infection in a given population. This study uses symptoms data collected in the Global COVID-19 Trends and Impact Surveys (UMD Global CTIS), and data on variants sequencing from GISAID. This work, conducted in January of 2022 during the emergence of the Omicron varia...
Biases in author recognition. The dynamics of remembering and forgetting
Baquero, Carlos; Cabecinhas, Rosa[Excerpt] Human memory does not correspond to the objective recollection of events or the simple storage of a fixed past. It is a selective process of permanent interpretation and reconstruction as a function of a given context. The dynamics of remembering and forgetting are shaped by various personal, societal and cultural factors, and are subject to various ‘biases’. Our perception of people and events is sha...
Estimating the COVID-19 prevalence in Spain with indirect reporting via open su...
Garcia-Agundez, Augusto; Ojo, Oluwasegun; Hernández-Roig, Harold A.; Baquero, Carlos; Frey, Davide; Georgiou, Chryssis; Goessens, MathieuDuring the initial phases of the COVID-19 pandemic, accurate tracking has proven unfeasible. Initial estimation methods pointed toward case numbers that were much higher than officially reported. In the CoronaSurveys project, we have been addressing this issue using open online surveys with indirect reporting. We compare our estimates with the results of a serology study for Spain, obtaining high correlations (...
State-machine replication for planet-scale systems
Enes, Vitor; Baquero, Carlos; Rezende, Tuanir França; Gotsman, Alexey; Perrin, Matthieu; Sutra, PierreOnline applications now routinely replicate their data at multiple sites around the world. In this paper we present Atlas, the first state-machine replication protocol tailored for such planet-scale systems. Atlas does not rely on a distinguished leader, so clients enjoy the same quality of service independently of their geographical locations. Furthermore, client-perceived latency improves as we add sites clos...
Higher-order patterns in replicated data types
Leijnse, Adriaan; Almeida, Paulo Sérgio; Baquero, CarlosThe design of Conflict-free Replicated Data Types traditionally requires implementing new designs from scratch to meet a desired behavior. Although there are composition rules that can guide the process, there has not been a lot of work explaining how existing data types relate to each other, nor work that factors out common patterns. To bring clarity to the field we explain underlying patterns that are common ...
Scalable eventually consistent counters over unreliable networks
Almeida, Paulo Sérgio; Baquero, CarlosCounters are an important abstraction in distributed computing, and play a central role in large scale geo-replicated systems, counting events such as web page impressions or social network “likes”. Classic distributed counters, strongly consistent via linearisability or sequential consistency, cannot be made both available and partition-tolerant, due to the CAP Theorem, being unsuitable to large scale scenario...
Efficient Synchronization of State-based CRDTs
Enes, Vitor; Almeida, Paulo Sérgio; Baquero, Carlos; Leitão, JoãoTo ensure high availability in large scale distributed systems, Conflict-free Replicated Data Types (CRDTs) relax consistency by allowing immediate query and update operations at the local replica, with no need for remote synchronization. State-based CRDTs synchronize replicas by periodically sending their full state to other replicas, which can become extremely costly as the CRDT state grows. Delta-based CRDTs...
Delta state replicated data types
Almeida, Paulo Sérgio; Shoker, Ali; Baquero, CarlosConflict-free Replicated Data Types (CRDTs) are distributed data types that make eventual consistency of a distributed object possible and non ad-hoc. Specifically, state-based CRDTs ensure convergence through disseminating the entire state, that may be large, and merging it to other replicas. We introduce Delta State Conflict-Free Replicated Data Types (delta-CRDT) that can achieve the best of both operation-b...
Global-Local view: Scalable consistency for concurrent data types
Akkoorath, Deepthi; Brandão, J.; Bieniusa, Annette; Baquero, CarlosConcurrent linearizable access to shared objects can be prohibitively expensive in a high contention workload. Many applications apply ad-hoc techniques to eliminate the need for synchronous atomic updates, which may result in non-linearizable implementations. We propose a new model which leverages such patterns for concurrent access to objects in a shared memory system. In this model, each thread maintains dif...